[PATCH v4.4, v4.9] usb: dwc3: gadget: delay unmap of bounced requests

[Felipe Balbi <felipe.balbi@linux.intel.com>]

From: Janusz Dziedzic <januszx.dziedzic@intel.com>

commit de288e36fe33f7e06fa272bc8e2f85aa386d99aa upstream.

In the case of bounced ep0 requests, we must delay DMA operation until
after ->complete() otherwise we might overwrite contents of req->buf.

This caused problems with RNDIS gadget.

Cc: <stable@vger.kernel.org> # v4.4 v4.9
Fixes: d62145929992 ("usb: dwc3: gadget: always unmap EP0 requests")
Signed-off-by: Janusz Dziedzic <januszx.dziedzic@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
---

cherry-picked, fixed up and compile tested

 drivers/usb/dwc3/gadget.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 5dc6bfc91f4b..ce603dcbd493 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -174,6 +174,7 @@ void dwc3_gadget_giveback(struct dwc3_ep *dep, struct dwc3_request *req,
 		int status)
 {
 	struct dwc3			*dwc = dep->dwc;
+	unsigned int			unmap_after_complete = false;
 
 	req->started = false;
 	list_del(&req->list);
@@ -182,11 +183,19 @@ void dwc3_gadget_giveback(struct dwc3_ep *dep, struct dwc3_request *req,
 	if (req->request.status == -EINPROGRESS)
 		req->request.status = status;
 
-	if (dwc->ep0_bounced && dep->number <= 1)
+	/*
+	 * NOTICE we don't want to unmap before calling ->complete() if we're
+	 * dealing with a bounced ep0 request. If we unmap it here, we would end
+	 * up overwritting the contents of req->buf and this could confuse the
+	 * gadget driver.
+	 */
+	if (dwc->ep0_bounced && dep->number <= 1) {
 		dwc->ep0_bounced = false;
-
-	usb_gadget_unmap_request(&dwc->gadget, &req->request,
-			req->direction);
+		unmap_after_complete = true;
+	} else {
+		usb_gadget_unmap_request(&dwc->gadget,
+				&req->request, req->direction);
+	}
 
 	trace_dwc3_gadget_giveback(req);
 
@@ -194,6 +203,10 @@ void dwc3_gadget_giveback(struct dwc3_ep *dep, struct dwc3_request *req,
 	usb_gadget_giveback_request(&dep->endpoint, &req->request);
 	spin_lock(&dwc->lock);
 
+	if (unmap_after_complete)
+		usb_gadget_unmap_request(&dwc->gadget,
+				&req->request, req->direction);
+
 	if (dep->number > 1)
 		pm_runtime_put(dwc->dev);
 }
-- 
2.11.0.295.gd7dffce1ce